Frequent use of the term "difficult patient" suggests the existence of a single, well-described group. However, in a literature review of 94 articles, Bauke Koekkoek, R.N., C.N.S., and colleagues found evidence to support the existence of three subgroups of such patients—"the unwilling care avoider," "the ambivalent care seeker," and the "demanding care claimer." The authors also found that past studies have offered four patient-level theoretical explanations for the perceived difficulty: chronicity, dependency, character pathology, and lack of reflective capabilities. However, some commentators have located the difficulty in the therapeutic relationship and have focused on the emotional struggles of transference and countertransference. Other observers have called attention to systemic and sociological factors—prejudice, labeling, and exclusion—as the major explanation for the difficulty of treating these patients. Mr. Koekkoek and his colleagues review interventions and approaches found to be helpful with this patient group (page 795). In a related Taking Issue commentary, David A. Adler, M.D., offers guidance and support to clinicians who work with difficult patients in systems that are ill prepared to provide the extensive long-term services that they need (page 767).